US3596619A

US3596619A - A lock stitch sewing machine having crescent-shaped bobbin

Info

Publication number: US3596619A
Application number: US542005A
Authority: US
Inventors: Ragnar William Winberg; Robert W Winberg; Paul N Winberg
Original assignee: Individual
Current assignee: Individual
Priority date: 1966-04-12
Filing date: 1966-04-12
Publication date: 1971-08-03
Anticipated expiration: 1988-08-03

Abstract

A sewing machine having a crescent-shaped bobbin case which receives a supply of bobbin thread which cooperates with a needle movable through a stitch-forming cycle and receiving a needle thread which provides a lock stitch sewing machine having an exceptionally large capacity bobbin.

Description

United States Patent 72 Inventors Rlgnlr wfllim winbgrg [50] Field Of 112/181, l 185, 189, l92,228,23l,232

1 15 W. Elder Ave.. Florll Park, N.Y. 1 1001;

[56] References Cited UNITED STATES PATENTS 9/1932 Hemleb Robert W. Winberg, 19 York Place,

Williston Park, N.Y. 11596; Paul N.

7/1944 Billington.....................

Primary Examiner-Herbert F. Ross Attorney- Amster & Rothstein w r a P 3 4 9 H 8 778 5 9 772 725 22 m 2 l X N v. m m 8 1 m 1 M5... M1 m wMA 0 N 0 C Am l1 2 RB [45] Patented Aug.3, 1971 [54] HAVING ABSTRACT: A sewing machine having a crescent-shaped 8 Chim 25 D F bobbin case which receives a supply of bobbin thread which cooperates with a needle movable through a stitch-forming [52] US. cycle and receiving a needle thread which provides a lock stitch sewing machine having an exceptionally large capacity bobbin.

112/189,]12/228, 112/232 [51] Ill, D051! 57/14 PATENTEU AUG 3 I97! SHEET 1 OF 5 FIG. I.

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mvawmns P4 GA/AR M lw/veepe ROBERT m Wl/VBEIPG P401. M WM/8ER6 BY Amm'lm arrow: 7;

A LOCK STITCH SEWING MACHINE HAVING CRESCENT-SHAPED BOBBIN The present invention relates generally to sewing apparatus and methods, and in particular to an improved method for forming a lockstitch and the provision of a lockstitch sewing machine having an exceptionally large capacity bobbin.

The well known lockstitch sewing machine includes a reciprocating needle movable through a stitch-forming cycle and adapted to receive a needle thread which cooperates with a bobbin having a supply of bobbin thread therein which rotates within a bobbin race. The reciprocation of the needle and the rotation of the bobbin are timed relative to each other such that the needle thread is cast about the bobbin within its race and interengaged with the bobbin thread to form successive stitches. The usual bobbin is of relatively limited capacity and is capable of receiving anywhere up to 60 to 80 yards of bobbin thread representing a supply of anywhere from several minutes to several hours of stitching time, depending on the particular stitching operation and stitching rate. With the modern relatively high-speed sewing machines capable of stitching rate of about 5,000 stitches per minute, an operator is usually required to make four or more bobbin changes during a normal working day. Separate and apart from the lost time represented by the necessity of changing bobbins, there is a tendency of such operators to change bobbins in advance of runout to avoid such runout and the attendant need to repair an incompleted stitch line or seam. This represents an effective shortening of the uninterrupted stitching interval and, to a minor extent, involves waste of the unused bobbin thread.

There exists a need for a practical and efi'ective means for increasing the capacity of such bobbins in a manner compatible with achieving high-speed lockstitch. As those skilledin this art appreciate, it is not practical to merely increase the size of the present bobbin and bobbin case to bring about a corresponding increase in the storage capacity thereof; andin any event, the minor increases in size which could be achieved consistent with realizing the stitching function would present no real substantial advantage over existing machines.

Broadly, it is an object of the present invention to provide an improved lockstitch sewing machine which is capable of continuous or intermittent operation over long periods of time without the necessity of replenishing or replacing the supply of bobbin thread. Specifically, it is within the contemplation of the present invention to provide an improved bobbin assembly which has an exceptionally large capacity compared to present day bobbins, yet it is compatible with the high-speed formation of lockstitches and seams of desirable characteristics and quality.

In accordance with apparatus aspects of-the invention, there is provided a sewing machine which includes a needle movable through a stitch-forming cycle and adapted to receive a needlethread and a crescent-shaped bobbin case-having leading and trailing ends spaced from each other and provided with an internal chamber which is adapted to receive a supply of bobbin thread. Provisions are made for mounting the bobbin case for rotation about a bobbin axis, with such mounting means being constructed and arranged to enable the needle thread to be cast about the leading end of the bobbin case, engaged with the bobbin thread and withdrawn from about the trailing end of the bobbin case. Drive means are provided for moving the needle and rotating the bobbin case in timed relation to each other such as to interengage the needle and bobbin threads and thereby form the well known lockstitch.

A typical bobbin embodying features of the present invention comprises a bobbin case which includes an internal chamber for receiving a relatively large supply of bobbin thread. The bobbin .case has a leading end sewing as a needle thread-engaging hook, an elongated crescent-shaped intermediate extent about which the needle threadis adapted to be cast for engagement with the bobbin thread and a trailing end from which the needle and bobbin threads may be withdrawn as interengaged to form an elemental stitch. Preferably, the crescent-shaped intermediate extent of the bobbin case is of substantially circular cross section and this cross secton is more or less comparable in overall dimensions to the diameter of a conventional bobbin case such that an undue obstruction is not presented to the needle thread during the stitch-forming operation, as will be subsequently appreciated. This is of paramount importance in developing an otherwise compatible tensioning and takeup mechanism for the needle thread which will not have a prohibitively long stroke or throw and attendant disadvantages which might otherwise interfere with the construction of a commercially acceptable lockstitch sewing machine. Although, as a practical matter, the present bobbin assembly functions, insofar as the remaining stitching mechanisms are concerned, like a conventional bobbin for a lockstitching sewing machine, the capacity of such bobbin is many fold that of such conventional bobbin due to the crescent or toroidal shape and its corresponding substantial circumferential extent.

In accordance with the method aspects of the present invention, a bobbin thread is formed into a crescent-shaped or substantially toroidal wound bobbin. The needle thread is formed into a bobbin-receiving -loop at a stitch-forming location whereupon the crescent-shaped bobbin is passed through the bobbin-receiving loop while the bobbin is orientedto present its minimum cross section to the loop. This interengages the needle and bobbin threads whereupon :the needle thread is drawn up to complete an elemental lockstitch. The bobbin is passed through theloop by rotation about its axis. In a practical application, the bobbin is turned through one revolution during the formation of the needle thread into the bobbinreceiving loop and through a second revolution to pass the bobbin completely through the bobbinreceiving loop. The bobbin thread is directed to one side of the bobbin during one revolution of a stitch-forming sequence and to the other side of the bobbin during the second revolution of such stitchforrning sequence.

The above brief description as well as further objects, features, advantages and otherinventive aspects of he present invention will be more fully appreciatedby reference to the following detailed description of a presently preferred, but nonetheless illustrative,.embodiment in accordance with the present invention, wherein:

FIG. 1 is a side elevational view, with'parts broken away and sectioned (and with the conventional presser foot, four-motion feed dog and related structure eliminated in the interest of simplicity) of a-lockstitch sewing machine illustrating features of the present invention;

FIG. 2 is a transverse section taken substantially along the line 2-2 of FIG. 1 and looking in the direction of the arrows, showing the details of the present machine and in particular the bobbin and bobbin mounting or race assembly, with other conventional sewing machine components being deleted in the interest of simplicity and clarity;

FIG. 3 is a sectional view, taken substantially along the line 3-3 of FIG. 2 and looking in the direction of the arrows, showing the bobbin case in elevation and its related mounting and race assembly, with the bobbin case being substantially in the same position as is illustrated in FIGS. 1 and 2;

FIG. 4 is a fragmentary plan view, with parts broken away,

.looking down on the bobbin case from the needle or stitchforming location;

FIG. 5 is a longitudinal sectional view, on an enlarged scale, showing typical details for the bobbin case having a supply of bobbin thread therein, with the dot-dash lines showing a breakaway position for a section of the bobbin case enabling access thereto for loading-the same with a supply of bobbin thread;

FIG. 6' is a fragmentary view of the inner periphery of the bobbin case contiguous to the point of egress of the bobbin thread and showing typical details for a bobbin thread-tensioning assembly.

FIGS. 7 through 16 inclusive are diagrammatic and schematic representations demonstrating the successive positions of the needle, the bobbin case and the needle thread tensioner during the formation of an elemental Iockstitch in accordance with the present invention;

FIG. 17 is a simplified diagrammatic showing of the hitch Iockstitch produced in accordance with the present invention when the instant sewing machine is set up to operate in the mode illustrated in FIGS. 7- 16 inclusive;

FIGS. !823 inclusive are diagrammatic and schematic representations demonstrating the successive positions of the needle, the bobbin case and the needle thread tensioner during the formation of a conventional lockstitch in accordance with the present invention; and

FIGS. 24 and 25 are schematic and diagrammatic representations illustrating the compensating twists which are imparted to the bobbin thread during each stitch-forming cycle, either during the hitch lockstitch mode illustrated in FIGS. 7-16 or in the regular Iockstitch mode illustrated in FIGS. 18-23, which precludes a material alteration in the characteristics of the bobbin thread incident to such stitch-forming operations.

Before making detailed reference to FIGS. 1 to 6 inclusive for a simplified version of a sewing machine 20 embodying features of the present invention, reference will be made to FIGS. 7 to 16 inclusive for a description of the successive related positions of the stitching mechanisms during the formation of an elemental Iockstitch of one type to enable a clear understanding of the present invention and its important ramifications in the sewing machine art. It is to be emphasized that the illustrative showing herein is merely intended to portray the basic mechanisms of a sewing machine which are required for incorporation of the present invention; and that many well known and varied modifications, improvements and additions will be made to complete todays modern, sophisticated, high-speed lockstitch sewing machine, as exemplified by those manufactured by the Singer Sewing Machine Company of which Model No. 251 is representative and those manufactured by Union Special of which Model No. 6410 is representative.

Referring first to FIG. 7, a needle 22 having an eye 22a is supported on the usual reciprocating needle bar 24. A needle thread T is passed from the eye 26a of a thread-tensioning and takeup device 26, thence to a thread guide 28 and then through the eye 22a of the needle 22. Disposed below the needle 22 and positioned to cooperate therewith is a crescent or toroidal-shaped bobbin case 30 which is arranged to rotate about its central axis. The bobbin case 30 contains a supply of bobbin thread B which is interengaged with the needle thread T to form Iockstitches S in the material assembly M, the latter being diagrammatically shown as being fed from right to left in FIG. 7 as indicated by the directional arrow. The feed of the material or work M is achieved by the usual cooperating presser foot and four-motion feed dog (not shown in the illustrative machine) which is conventional in sewing machines of this type.

Intermediate the bobbin case 30 and below the location of the material or work M, there is provided a bobbin thread positioner 32 which serves as a means during each stitch-forming cycle for alternately directing the bobbin thread to the opposite sides of the leading end 30a of the bobbin case 30 such that compensating twists are imparted to the bobbin thread during the two revolutions of the bobbin case in each stitchforming cycle. Practical experience with this new stitching technique reveals that a cumulative twisting or untwisting would be imparted to the bobbin thread B (depending upon the direction of the original twist and the initial orientation of the bobbin thread B during the stitching operation) which would either impart further twist to the bobbin thread B or remove twist therefrom during the stitching operation, both with deleterious effects. Thus, the bobbin thread positioner 32 functions to preclude any accumulation of twisting or untwisting of the bobbin thread B during the stitching operation. The same general parts are shown in FIGS. 7 to 16 inclusive in successive positions of orientation relative to each other. Now progressive reference will be made to these figures for the description of a typical stitch-forming cycle which involves the reciprocation of the needle 22 through its downward and upward strokes and two complete rotations of the bobbin case 30, with the necessary coordinated movements'of the needle thread tensioning and takeup device 26 and the bobbin thread positioner 32.

The FIG. 7 position illustrates what can be conveniently designated as a starting position wherein the previous stitch has just been completed, the needle 22 is in its fully retracted position, the takeup or thread tensioner 26 is in its fully retracted position having drawn the previously completed stitch S tight and the point of egress 30d of the bobbin thread B from the bobbin case 30 is at the maximum displacement from the stitch-forming location. It is only practical to complete the stitch S by drawing the stitch up tight when the maximum free length of bobbin thread B has been established, for otherwise there would be no reaction force presented by the spring-tensioned bobbin thread B to the pull afforded by the thread tensioner 26 incident to the stitch-forming operation.

In the FIG. 7 position, with the needle 22 full-up, the thread tensioner 26 full-up, the bobbin case 30 symmetrically disposed relative to the vertical needle path and the needle 22 directed substantially towards the center of the clearance space between the leading and trailing

ends

30a, 30b, respectively, of the bobbin 30, a stitch-forming cycle is about to commence. For this illustrative starting position, the bobbin thread positioner 32 is disposed in relation to the plane of symmetry of the bobbin case 30 to direct the bobbin thread B to the far side of the bobbin case 30 (when viewed from the left end of the machine), as may be best appreciated by progressive reference to FIGS. 7 and 8. As seen in FIG. 8, the material M advances through the stitch length increment (established by the conventional presser foot and feed dog) and the needle 22 penetrates the material at the new stitchforming location. Concurrently, the bobbin case 30 rotates in the counterclockwise direction and in the direction of material feed, with the bobbin thread B passing to the far side of the bobbin case in a slack condition. The needle 22 continues its downward stroke going through the intermediate'position of FIG. 9 into the full-down position illustrated in FIG 10 wherein the bobbin thread B is drawn substantially taut in that its point of egress 30d from the bobbin case 30 is at the maximum displacement from the stitch-forming location. In the FIG. 10 position, the leading end 30a of the bobbin case 30, which serves as a needle thread-engaging hook, approaches the needle thread T which includes a segment T (to the right of the needle when viewed from the front of the machine and behind the needle in FIG. 10) which segment extends down through the work or material M and the needle eye 22a. Accordingly, as may be best appreciated by comparing FIGS. 10 and 11, the hook 30a is capable of penetrating behind the needle 22 into the hook-receiving space between the needle 22 and the thread segment T,. This passes the needle thread T about the bobbin case 30, which is of progressively increasing substantially circular cross section from its leading end 30a, until the same merges into the intermediate body proper 300 which is of substantially uniform circular cross section throughout a major portion of its circumferential extent. In the FIG. 10 position, the bobbin thread B is engaged by the bobbin thread positioner 32 (not shown in FIG. 10 in the interest of clarity) which is laterally adjusted into relation to the plane of symmetry of the bobbin case 30 to cause the bobbin thread B to pass to the front or near side of the bobbin case during continued rotation thereof, as may be appreciated by progressively inspecting FIGS. 11 and 12. As seen in FIGS. 7

to 10 inclusive, the bobbin case 30 has made one complete rotation as the needle 22 moves from the fully retracted posi tion of FIG. 7 to the fully extended position of FIG. 10; and during such rotation a twist is imparted to the bobbin thread as seen clearly in FIG. 9 and illustrated diagrammatically in FIG.

24. Accordingly, when the bobbin thread is displaced to the opposite side of the bobbin case, and as may be appreciated by progressively inspecting FIGS. 11 to 13, a compensating twist (see FIGS. 13 and 25) is imparted to the bobbin thread. This nullifies the twist imparted during the first rotation as the bobbin thread completes its second revolution in the stitch-forming cycle.

continuing with the description of the stitch-forming sequence, during the initail part of the second cycle of rotation of the bobbin case 30, the needle thread T is relaxed in that the thread tensioner 26 has moved downwardly, as may be appreciated by progressively inspecting FIGS. to 13 inclusive. This enables the needle thread T to be cast about the bobbin case 30, as seen in FIGS. 11 to 13. As the bobbin case 30 continues to rotate in the counterclockwise direction, the point of egress 30d of the bobbin thread B and the corresponding portion of the bobbin case 30 is drawn through the elemental thread loop T cast about the bobbin case 30. As may be appreciated by progressively inspecting FIGS. 12 to 14 inclusive, this in turn effectively completes the interengagement of the bobbin thread B and needle thread T which then may be cast off of the bobbin case, as seen in FIGS. 14 and 15. As the bobbin case 30 completes its second rotation in the stitchforming cycle, the thread tensioner 26 commences to move upwardly through its tensioning stroke, as may be seen by progressively inspecting FIGS. 14 to 16 inclusive. Throughout this time, as may be seen in FIGS. 11 to I6 inclusive, the needle 22 has moved from the fully penetrated position illustrated in FIG. 10 to the fully retracted position illustrated in FIG. 7 (the FIG. 16 position being just prior to the needle being fully retracted). As shown in FIGS. 16 and 7, as the bobbin case 30 returns to the FIG. 7 position and the thread tensioner 26 returns to its fullup position, the next stitch S is completed. Thereupon, the foregoing operations are repeated, with the needle 22 moving through its forward and return strokes in timed relation to the two revolutions of the bobbin case 30, to complete further lockstitches.

For the mode of operation illustrated diagrammatically in FIGS. 7 to 16 inclusive, it will be appreciated that the bobbin case 30 is rotating in the counterclockwise direction (see the directional arrows in the successive figures). (Ioncurrently, the material M is moved stepwise in the usual direction from the front of the sewing machine toward the back thereof, as indicated by the directional arrow in FIG. 7 and the progression of the material M in the successive figures. For such counterclockwise rotation of the bobbin case 30 and advance of the leading end 30a thereof substantially in the direction of material feed, a special lockstitch configuration is attained, as seen best in FIG. 16 and in the enlarged showing of FIG. 17. This special stitch configuration, which may be characterized as a hitch lockstitch, involves the formation of a bobbin thread loop L about the needle or top thread T which may be desirable fir certain applications. The very nature of the illustrated hitch lockstitch, which is characterized by the bobbin thread B being looped or wrapped about the needle thread T, contributes materially to strengthening the overall stitch line, without detracting from the appearance or other characteristics thereof.

If in lieu of the hitch lockstitch produced in accordance with the mode of operation illustrated in FIGS. 7-17 inclusive, a conventional lockstitch is desirable, one method of achieving such a result is to establish a direction of rotation for the bobbin case 30 which is opposite to that illustrated in FIGS. 7-17. Specifically, for the direction of material feed illustrated in the drawings (right to left indication feed from in front of the needle to the back thereof as is conventional in sewing machines), a clockwise direction of rotation may be imparted to the bobbin case 30 to attain a conventional lockstitch. The formation of such conventional lockstitch will now be described in connection with the progressive and diagrammatic showings of FIGS. 18-23. The FIG. 18 position (generally corresponding to FIG. 7) may be considered to be the starting position wherein the previous stitch has just been completed. The needle 22 has commenced its downward or material-penetrating stroke, the takeup or thread tensioner 26 (not shown) is substantially in its fully retracted position and the point of egress 30d of the bobbin thread B from the bobbin case 30 has just passed its maximum displacement from the stitch-forming location. As before, the bobbin thread positioner 32 is disposed in relation to the plane of symmetry of the bobbin case 30 to direct the bobbin thread B to the far side of the bobbin case 30 (when viewed from the left end of the machine), as may be best appreciated by progressive reference to FIGS. 18 and 19. In the FIG. 18 position, the material M has just advanced through its stitch length increment and the needle 22 is penetrating the material M at the new stitch-forming location. The concurrent clockwise rotation of the bobbin case 30 opposite to the direction of material feed causes the bobbin thread B to pass to the far side of the bobbin case in a slack condition. The needle 22 continues its downward stroke moving into its full-down position which, although not specifically illustrated, occurs between the positions illustrated in FIGS. 19 and 20. At the full-down position, the bobbin thread B is once again drawn taut in that its point of egress 30d from the bobbin case 30 is at the maximum displacement from the stitch-forming location. Thereupon, the leading end 30a of the bobbin case 30, which serves as the needle thread-engaging hook, penetrates between the far side of the needle (to the right of the needle when viewed from the front of the machine) and is received within the corresponding hook-receiving space. Thus, the hook or leading end 30a passes the needle thread T about the bobbin case 30, as may be appreciated by progressively inspecting FIGS. 20 to 23, to complete a conventional lockstitch. As was the case with the mode of operation illustrated in FIGS. 7--16 inclusive, during the first rotation of the bobbin case 30, a first twist is imparted to the bobbin thread B and during its second rotation during the stitch-forming cycle a compensating twist is imparted thereto (see FIGS. 24 and 25). Once again, the oppositely directed twists during the first and second rotations of the bobbin case compensate each other and the stitch-forming cycle is completed without altering the characteristics of the bobbin thread.

From the foregoing generalized description, it will be appreciated that the present invention enables the provision of either a so-calledhitch lockstitch or a conventional lockstitch. The description which follows is of a typical, yet illustrative, machine wherein the direction of rotation of the bobbin case 30 is such as to provide the hitch lockstitch.

Reference will now be made to FIGS. 1 to 6 inclusive for a detailed description of an illustrative sewing machine 20 capable of embodying either of the foregoing stitch-forming methods. The sewing machine 20 includes a bed plate or casting 34 providing a work-supporting surface 34a over which the material or work M passes. The bed plate 34 supports the usual sewing machine housing 36 (see FIG. 1) which includes a standard 36a at the right end of the machine (when viewed from the front), a horizontally extending overhanging arm 36b and a head 360 at the stitching location. The head 36c overlies the conventional throat plate 38 supported in the feed bed 34 (see FIG. 2) and provided with the needle hole 380. Extending lengthwise of the arm 36!), through the standard 36a and into the head 36c, is the usual mainsewing machine shaft 40 (see FIG. 1). The main shaft 40 projects externally of the housing 36 at the drive end thereof and is coupled via the usual belts and pulleys to an appropriate sewing machine motor (not shown). Supported in the head 36c is the usual reciprocating needle bar 24 which is actuated from the main shaft 40 by conventional means including a combined needle and takeup cam 42 which is keyed to the main shaft 40. The cam '42 carries the usual eccentric pin 44 which is coupled by link 46 and pivot 48 to the connecting block 50 on the reciprocable needle bar 24. Overlying the peripheral camming surface 420 of the cam 42 is the usual tensioning and takeup lever 52 which is pivoted within the housing at pivot 54. Lever 52 carries camengaging follower 56 and extends forwardly through opening 36d in the head 36c, terminating in the described takeup 26 which servesthe usual thread-tensioning and takeup functions during thelockstitch-forming cycle. As is also conventional, provision is made on the head 360 for tensioning the thread in advance of its passage through the eye 26a in the takeup 26 after which the thread T passes downwardly through the thread guide 28 to the eye 22a of the needle 22. The known thread-tensioning device, which is generally designated by the reference numeral 58, includes frustoconical tensioning plates 58a, 58b which are spring-biased by the coil spring 580, provision being made for adjusting the tension on spring 580 by nut 58d. The contour of the peripheral cam surface 42a is such that cam follower 56 on the lever 52 will cause the takeup 26 to move up and down in accordance with the general requirements imposed for a lockstitch sewing machine. Although not illustrated, it will be appreciated that within the head 360 of the sewing machine, there is provided the usual presser foot bar which carries a presser foot which cooperates with the four-motion feed dog disposed below the throat plate 38. The feed dog is accessible through appropriate cutouts in the throat plate 38 for feeding the work past the stitching location. Since many aspects of the sewing machine heretofore described are conventional and subject to a wide variation of latitude and change as is generally understood by those skilled in this art, further detailed description is not required and is dispensed with in the interests of brevity.

Disposed below the feed bed 34 in spaced parallel relation to the main shaft 40 is a bobbin shaft 60 (see FIG. 2) which is joumaled on appropriate bearings for rotation, as indicated by the directional arrows of FIGS. 1 and 2. The bobbin shaft is driven in a two-to-one ratio to the main shaft 40 by a timing belt 64 (see FIG. 1) and appropriate interconnecting pulleys, as is generally understood for sewing machines of this type. The driven bobbin shaft 60 terminates substantially in the vertical plane in which the needle 22 reciprocates, which vertical plane is, for all practical intents and purposes, the plane of symmetry of the bobbin case 30. As will now be described, the bobbin case is supported to rotate about the axis of the bobbin shaft 60 within its plane of symmetry and in a common vertical plane with the reciprocating needle 22.

The bobbin case is joumaled for rotation in its plane of symmetry by bobbin-mounting means, generally designated by the reference numeral 66, which includes opposed or right and left race-forming

assemblies

68, 70. The right race-forming assembly 68 is mounted on the bobbin shaft 60, while the left race-forming assembly 70 is mounted on a stub shaft 72 which is supported in end-to-end alignment with the bobbin shaft 60. The stub shaft 72 is held on a support 74 depending from the bed plate or casting 34 and provided with a circular guideway 74a receiving the adjacent end of stub shaft 72. The stub shaft 72, which is ordinarily secured in the position illustrated in FIG. 2, is retractable toward the left as illustrated in FIG. 2, by the directional arrows, to enable the bobbin case 30 to be removed form the bobbin-mounting means 66. To this end, the stub shaft 72 is provided with a keyway 72a which receives the leading threaded end 760 of a locking key 76 which is received within a threaded hole 74b in support 74. It will, of course, be appreciated that other and perhaps more sophisticated arrangements may be provided for securing the stub shaft 72 in the illustrated position and permitting its lengthwise displacement for removing the bobbin case 30 from within the bobbin-mounting means 66.

The right race-forming assembly 68 is seen to include a rotatable follower carrier 78 which is connected to the shaft 60. Disposed inwardly of the follower carrier 78 on the adjacent terminal end of the shaft 60 is a floating cheek plate 79 which is formed at its inner side with an appropriately contoured face 790. The contoured face 79a includes a planar medial section which extends substantially in the plane of symmetry of the bobbin case and appropriately contoured margins to be received within the journaling for the bobbin case. The left race-forming assembly 70 includes a rotatably follower carrier 80 which is loosely joumaled on the shaft 72. Disposed inwardly of the follower carrier 80 is a cheek plate 81 which is I formed at its inner side with an appropriatelycontoured face lo joumaled and the left side (cheek plate 81) being stationary.

The clearance space between the

faces

79a, 81a provides an unobstructed path for the passage of the bobbin thread B from the point of egress 30d from the bobbin (see FIG. 2).

The follower carrier 78 is keyed to the bobbin shaft 60 by locking key 82 to be driven by such bobbin shaft, while the follower carrier is loosely joumaled on the stub shaft 72 and is confined against longitudinal displacement in one direction by the fixed cheek plate 81 and in the opposite direction by the remaining mechanisms of the left race-forming assembly 70, as will be subsequently described.

Provision is made for supporting the bobbin case 30 at a plurality of spaced circumferential external locations in a manner such that a clear and unobstructed path may be afforded for the needle thread T as the latter is cast about the leading end 30a of the bobbin case 30 and is engaged with the bobbin thread B to complete either of the described stitchforrning sequences. To this end, the follower carrier 78 supports three radially

reciprocable supporting fingers

84, 86, 88. Seen best in FIGS. 2 and 3, the

fingers

84, 86, 88 are disposed at positions approximately corresponding to 12 oclock, 4 oclock and 8 o'clock, are spaced apart by 120 and afford corresponding peripheral point supports for the bobbin case 30. The

fingers

84, 86, 88 are of similar construction and accordingly it will suffice to describe only one in detail. For example, finger 84, seen in FIG. 2, is L-shaped and includes a first arm 84a which is mounted in a corresponding radial guideway 78b in carrier 78 and a second arm 84b which terminates in a spherical supporting finger 840. The supporting finger 84c is normally disposed in a spherical seat 30e provided at the corresponding circumferential location of the bobbin case 30. Thus, as a practical matter, there is provided an essentially tripod support for the right side of the bobbin case. Similarly, the follower carrier 80 of the left race-forming assembly 70 includes three fingers 90, 92, 94 (see FIGS. 1 and 2) which are spaced at 120 relative to each other and engage the left side of the bobbin case 30 at locations approximately corresponding to 2 o'clock, 6 oclock and 10 o'clock. Accordingly, for this illustrative bobbin-mounting means 66, effective support is provided for the bobbin case at opposite sides thereof and at 60 intervals.

Provision is made for extending the successive supporting

fingers

84, 90, 88, 92, 86 and 94 to clearance positions as they are driven to the stitch-forming location, a typical clearance position being illustrated for finger 84 in FIG. 2. With the successive finers thus lifted and the required space afforded at the inner side of the bobbin case by the appropriately contoured bearing faces 79a, 81a, the unobstructed casting of the needle thread T about the bobbin 30 and interengagement with the bobbin thread B may be accomplished. To this end, the right race-forming assembly 68 includes a stationary cam 96 which is mounted on the bed plate 34 and through which the driven bobbin shaft 60 freely extends. The stationary cam 96 is provided with a cam track 96a at its inner face contiguous to the follower carrier 78. The cam track 96a receives corresponding cam followers 98, 100 and 102 (see H68. 2 and 3) for the

fingers

84, 86, 88. The left race-forming assembly likewise includes a stationary cam 104 which is secured to the stub shaft 72 by the locking element 106 and is provided with cam track 104a in the face contiguous to the left follower carrier 80. ln turn, each of the fingers 90, 92, 94 carriers a cam follower (see follower 108 for finger 92 in H0. 2) which are engaged within the cam track 104a in stationary cam 104. The developments of the cam tracks 96a, 104a are substantially identical and are arranged, as shown in the dotted lines in FIG. 1, to successively move the supporting fingers to clearance positions relative to the bobbin case 30. Although there is illustrated but one bobbin-mounting means 66 which enables the needle thread T to be cast about the leading end of the bobbin case 30, engaged with the bobbin thread B and withdrawn from trailing end of the bobbin case to complete the described stitch-forming sequences, it will be appreciated by those skilled in the art that there are many different and generally known arrangements which will sufl'ice to mount a bobbin case in a manner appropriate for the practice of the present invention. The important characteristics of such bobbin-mounting mechanism is the provision of an unobstructed path for the bobbin thread B in the plane of symmetry of the bobbin case (which in this illustrative embodiment is afforded by the clearance space between the

faces

79a, 81a of the carriers 78, 80), the ability to direct such bobbin thread to one side or the other side of the bobbin case at the stitch-forming location (the bobbin thread as being directed toward the right in the illustrative showing of FIG. 2) and the facility to cast the needle thread T about the bobbin case at the stitch-forming location.

In this illustrative arrangement, the bobbin thread positioner 32 is mounted beneath the bed plate 34 for the displacement laterally of the material feed path and at a-plane to engage the bobbin thread B, as seen best in FIGS. 2 and 4. The bobbin thread positioner 32 terminates at its leading end in a finger 320 which generally extends in the direction of material feed andalso in the direction of bobbin rotation. Finger 32a of positioner 32 is arranged to be shifted first to one side and then to the other side of the plane of symmetry of the bobbin case 30 and of the thread-engaging hook 300 thereof. In the detailed showing of FIG. 2, the finger 32a is to the left of the vertical plane of the needle 22 and of the hook 300. Accordinz y, the book will pass the bobbin thread to the corresponding left side of the bobbin case 30. In the fragmentary and illustrative showing in FIG. 4, the finger 32a is to the right of the hook and the needle location (represented by the needle hole 380 in the throat plate 38). Accordingly, the bobbin thread passed to the right of the bobbin case 30. The bobbin thread positioner 32 is normally biased toward the left, as seen in FIG. 2, by provision of a spring 110 which is anchored at one end on the stationary cam 96 and is connected at its other end to the laterally reciprocable positioner 32. Provision is made to actuate the thread positioner toward the right in FIG. 2 (and into the FIG. 4 position) at the end of the first rotation of the bobbin case 30 in the stitch-forming cycle by the provision of an actuating lever l 12 which is pivoted intermediate its ends at pivot 114 on the frame. The upwardly directed arm 112a of the lever 112 has a pivotal connection 116 to the adjacent rearward end of the thread positioner 32, while the downwardly directed arrn 112!) carries a cam follower 118 which engages a rise portion 1200 on cam 120 which is journaled by integral stub 12% on a depending bearing 122 on bed plate 34. The periphery of the cam 120 is formed with an integral gear lc which meshes with a positioner-actuating gear 124 secured to the bobbin shaft 60. The gearing ratio afforded by the meshing gears 124, 1200 is two to one such that during each two revolutions of the bobbin shaft 60, there will be a single-lateral displacement of the thread positioner 32 in accordance with the present invention. Here, again, various mechanisms are available for selectively positioning the bobbin thread B to one side or the other of the bobbin case 30.

Referring now to FIGS. 4 and 6, the bobbin case 30 is seen to include the body proper 30c of substantially uniform circular cross section. In one direction, the cross section progressively decreases and tenninstes at the needle thread-engaging hook 30a. At its opposite trailing end, the body proper 300 is of a somewhat reduced cross section appropriate for casting oil of successive completed stitches. The part of the bobbin case 30 which is of diminishing cross section and merges in the bobbin hook 300 is designated by the reference 30f and is seen to be hinged at 303 to the main part 301: of the bobbin case to permit access to the internal chamber 301' which houses a correspondingly crescent-shaped wound bobbin or supply B. When the hinged part 30f isswung to the breakaway position illustrated by the dot-dash lines in FIG. 5, access may be had to the internal chamber 30i for loading and reloading the supply of bobbin thread B. Any convenient arrangement may be provided for securing the hinged part 30f to the main part 3011, as by catch 30] which is secured to the hinged part on 30f contiguous to the breakaway or parting joint and extends lengthwise into the corresponding end of the main part 30h wherein it is engaged with an internal keeper formed in the main section 30h. A catch-release opening 30k may be provided in the inner periphery of the bobbin case contiguous to the catch 30] for depressing the catch to release the same, permitting the hinged part 30] to be swung towards the open position. The bobbin thread is peeled off the cone-shaped leading end of the bobbin supply B, is passed about the guide pin 301, fee back along the inner periphery of the bobbin case and then exits through opening 30m provided in the base of a depressed well 30n formed in the bobbin case at a point diametrically opposed from the clearance space between the leading and trailing

ends

30a, 30b. Disposed within the well 30m is a bobbin thread-tensioning spring 30p which is riveted or otherwise secured to the bobbin case. As seen best in FIG. 6, the bobbin thread B passes from the opening 30m and-then beneath the spring 30p whereupon it egresses to be drawn toward the stitch-forming location.

A typical sequence of operations will now be described briefly in order to further facilitate an understanding of the present invention:

The bobbin case 30 is broken open, as illustrated in FIG. 5 and loaded with a supply of bobbin thread B. After passing such supply about the guide 301, into the opening 30m and engaging the same beneath the tensioning spring 30p, the bobbin is closed and is ready for insertion into the machine. This is accomplished by releasing the stub shaft 72 and displacing the same toward the left (see FIG. 2). After the bobbin case is placed between the right and left race-forming

assemblies

66, 70, the bobbin-mounting means 70 is reengaged. The bobbin thread is brought into a position wherein it can be picked up by the needle 22, as is conventional in the threading of any sewing machine, and the work goes forward with successive stitches being completed as described in conjunction with the diagrammatic showings of either FIGS. 7 to 16 inclusive or FIGS. 18 to 23. During the stitching operation, the toroidal or crescent-shaped bobbin presents a minimal cross section for formation of the lockstitch, yet afi'ords a relatively large supply of bobbin thread (i.e., 20 fold that of any conventional bobbin). Since the throw of the combined thread tensioning and takeup device 52 is directly related to the necessary feed and takeup of the needle thread T during the stitch-forming operation, it will be appreciated that the conventional thread tensioning and takeup mechanisms may be designed within usual and accepted limits. The present stitch-forming operation merely involves casting about the cross section of the bobbin and is not appreciably changed notwithstanding the fact that the bobbin has a substantial circumferential extent.

The present stitching technique and mechanisms assure the formation of lockstitch seams having excellent characteristics. The mechanisms are designed such that the twist imparted to the bobbin during the successive stitch-forming cycles are compensated within each cycle thereby avoiding the twisting or untwisting of the bobbin thread. The tightness of the seam can be regulated in accordance with well accepted and conventional means in that the present unit is designed to form the stitches while the maximum free length of the bobbin thread drawn out during any stitch-forming cycle is under tension. This provides the necessary reaction force for use of a conventional sewing machine needle thread-tensioning device. The paths of the needle and bobbin threads are such that there are relatively no abrupt changes in thread direction, a characteristic which is important to afford minimal inertial forces and abrasive action incident to the stitching operation.

This assures less needle thread breakage and makes possible operation at the required high speed. The bobbin thread is wound in a manner such that it is in the form of a self-supporting cone which is generally crescent-shaped and will provide a supply of bobbin thread, with little or no tendency to overrun or afford backlash another contributing factor to the proper functioning of the sewing machine. Finally, the overall machine design is such that an optimal stitch configuration may be realized in accordance with the present invention. Optimally, the cross over between the needle and bobbin thread should be within thickness of the material or work rather than in a position wherein the needle thread penetrates all the way through the work and is caught by the bobbin thread at the under side of the material assembly. Experience with the present stitching mechanism indicates that by appropriate tension adjustment, it is possible to assure an interlocking of the needle and bobbin threads substantially midway between the top and bottom of the several plies of material being stitched.

We claim:

1. In a sewing machine, a needle movable through a stitchforming cycle and adapted to receive a needle thread, a crescent-shaped bobbin case having leading and trailing ends spaced from each other and an internal chamber adapted to receive a supply of bobbin thread therein, means mounting said bobbin case for rotation about a bobbin axis, said mounting means being constructed and arranged to enable said needle thread to be cast about said leading end of said bobbin case, engaged with said bobbin thread and withdrawn from about said trailing end of said bobbin case, said mounting means including spaced members for supporting said bobbin case at a plurality of spaced locations circumferentially thereof and means for periodically moving said members to a clearance position relative to said bobbin case to enable said needle thread to be cast about said bobbin case and drive means for moving said needle and rotating said bobbin case in timed relation to each other.'

2. A sewing machine according to claim 1 wherein said drive means is arranged to rotate said bobbin case through two revolutions during each stitch-forming cycle.

3. A sewing machine according to claim 2 including means operable during each stitch-forming cycle for alternately directing said bobbin thread to the opposite sides of said leading end of said bobbin case such that compensating twists are imparted to said bobbin thread during the two revolutions of said bobbin case in each stitch-forming cycle.

4. A sewing machine comprising a needle movable through a stitch-forming cycle and adapted to receive a needle thread and present the same at a stitch-forming location, a crescentshaped bobbin case having leading and trailing ends spaced from each other, an internal chamber adapted to receive a supply of bobbin thread therein and an exit port from said internal chamber providing a dispensing location disposed diametrically in relation to the space between said leading and trailing ends, means mounting said bobbin case for rotation about a bobbin axis, said mounting means being constructed and arranged to enable said needle thread to be case about said leading end of said bobbin case, engaged with said bobbin thread and withdrawn from about said trailing end of said bobbin case, said bobbin thread being withdrawn from said bobbin case incident to rotation thereof and presenting its maximum free length of said bobbin thread when said dispensing location is at its corresponding maximum spacing from said stitch-forming location, said leading end of said bobbin case serving as a hook and engaging said needle thread at said stitch-forming location, tensioning means engaging said needle thread and periodically operable for drawing up on the interengaged needle and bobbin threads when said threads are withdrawn from about the trailing end of said bobbin case and while said dispensing location is substantially at its maximum spacing from said stitch-forming location and coordinated drive means for reciprocating said needle, rotating said bobbin case and actuating said tensioning means in timed relation to each other, wherein said drive means is arranged to rotate said bobbin case through two revolutions during each stitch-forming cycle, means operable during each stitch-forming cycle for alternately directing said bobbin thread to the opposite sides of said leading end of said bobbin case such that compensating twists are imparted to said bobbin thread during the two revolutions of said bobbin case in each stitch-forming cycle.

5. A-method of forming a lock stitch with a needle thread and a bobbin thread comprising the steps of forming said bobbin thread into a crescent-shaped bobbin, forming said needle thread into a bobbin-receiving loop at a stitch-forming location, rotating said bobbin to pass said bobbin through said loop while said bobbin is oriented to present its minimum cross section to said loop to interengage said needle and bobbin threads and drawing up said needle thread .to complete said lock stitch, said bobbin being turned through one revolution during formation of said needle thread into said bobbinreceiving loop and through a second revolution to pass said bobbin completely through said bobbin-receiving loop, said bobbin thread being directed to one side of said bobbin during said one revolution and to the other side thereof during said second revolution.

6. In a sewing machine, a needle movable through a stitchforming cycle and adapted to receive a needle thread, a crescent-shaped bobbin case having leading and trailing ends spaced from each other and an internal chamber adapted to receive a supply of bobbin thread therein, means mounting said bobbin case for rotation about a bobbin axis, said mounting means being constructed and arranged to enable said needle thread to be cast about said leading end of said bobbin case, engaged with said bobbin thread and withdrawn from about said trailing end of said bobbin case, drive means for moving said needle and rotating said bobbin case in timed relation to each other, said drive means being arranged to rotate said bobbin case through two revolutions during each stitch-forming cycle, and means operable during each stitchforming cycle for alternately directing said bobbin thread to the opposite sides of said leading end of said bobbin case such that compensating twists are imparted to said bobbin thread during the two revolutions of said bobbin case in each stitchforming cycle.

7. A sewing machine comprising a needle movable through a stitch-forming cycle and adapted to receive a needle thread and present the same at a stitch-forming location, a crescentshaped bobbin case having leading and trailing ends spaced from each other, an internal chamber adapted to receive a supply internal bobbin thread therein and an exit port from said internal chamber providing a dispensing location disposed diametrically in relation to the space between said leading and trailing ends, means mounting said bobbin case for rotation about a bobbin axis, said mounting means including circumferentially spaced mounting members constructed and arranged to enable said needle thread to be cast about said leading end of said bobbin case, engaged with said bobbin thread and withdrawn from about said trailing end of said bobbin case, said bobbin thread being withdrawn from said bobbin case incident to rotation thereof and presenting its maximum free length of said bobbin thread when said dispensing location is at its corresponding maximum spacing from said stitch-forming location, said leading end of said bobbin case serving as a hook and engaging said needle thread at said stitch-forming location, tensioning means engaging said needle thread and periodically operable for drawing up on the interengaged needle and bobbin threads when said threads are withdrawn from about the trailing end of said bobbin case and while said dispensing location is substantially at its maximum spacing from said stitch-forming location and coordinated drive means for reciprocating said needle, rotating said bobbin case and actuating said tensioning means in timed relation to each other, wherein said driving means is arranged to rotate said bobbin case through two revolutions during each stitchforming cycle and including means operable during each stitch-forming cycle for alternately directing said bobbin thread to the opposite sides of said leading end of said bobbin case such that compensating twists are imparted to said bobbin thread during the two revolutions of said bobbin case in each stitch-forming cycle.

8. A sewing machine comprising a needle movable through a stitch-forming cycle and adapted to receive a needle thread and present the same at a stitch-forming location, a crescentshaped bobbin case having leading and trailing ends spaced from each other, an internal chamber adapted to receive a supply of bobbin thread therein and an exit port from said internal chamber providing a dispensing location disposed diametrically in relation to the space between said leading and trailing ends, means mounting said bobbin case for rotation about a bobbin axis, said mounting means including circumferentially spaced mounting members constructed and arranged to enable said needle thread to be cast about said leading end of said bobbin case, engaged with said bobbin thread and withdrawn from about said trailing end of said bobbin case, said bobbin thread being withdrawn from said bobbin case incident to rotation thereof and presenting its maximum free length of said bobbin thread when said dispensing location is at its corresponding maximum spacing from said stitchforming location, said leading end of said bobbin case serving as a hook and engaging said needle thread at said stitch-forming location, tensioning means engaging said needle thread and periodically operable for drawing up on the interengaged needle and bobbin threads when said threads are withdrawn from about the trailing end of said bobbin case and while said dispensing location is substantially at its maximum spacing from said stitch-forming location and coordinated drive means for reciprocating said needle, rotating said bobbin case and actuating said tensioning means in timed relation to each other, wherein said mounting means includes means for periodically moving said mounting members to a clearance position relative to said bobbin case to enable said needle thread to be cast about said bobbin case.

Claims

1. In a sewing machine, a needle movable through a stitchforming cycle and adapted to receive a needle thread, a crescentshaped bobbin case having leading and trailing ends spaced from each other and an internal chamber adapted to receive a supply of bobbin thread therein, means mounting said bobbin case for rotation about a bobbin axis, said mounting means being constructed and arranged to enable said needle thread to be cast about said leading end of said bobbin case, engaged with said bobbin thread and withdrawn from about said trailing end of said bobbin case, said mounting means including spaced members for supporting said bobbin case at a plurality of spaced locations circumferentially thereof and means for periodically moving said members to a clearance position relative to said bobbin case to enable said needle thread to be cast about said bobbin case and drive means for moving said needle and rotating said bobbin case in timed relation to each other.

4. A sewing machine comprising a needle movable through a stitch-forming cycle and adapted to receive a needle thread and present the same at a stitch-forming location, a crescent-shaped bobbin case having leading and trailing ends spaced from each other, an internal chamber adapted to receive a supply of bobbin thread therein and an exit port from said internal chamber providing a dispensing Location disposed diametrically in relation to the space between said leading and trailing ends, means mounting said bobbin case for rotation about a bobbin axis, said mounting means being constructed and arranged to enable said needle thread to be case about said leading end of said bobbin case, engaged with said bobbin thread and withdrawn from about said trailing end of said bobbin case, said bobbin thread being withdrawn from said bobbin case incident to rotation thereof and presenting its maximum free length of said bobbin thread when said dispensing location is at its corresponding maximum spacing from said stitch-forming location, said leading end of said bobbin case serving as a hook and engaging said needle thread at said stitch-forming location, tensioning means engaging said needle thread and periodically operable for drawing up on the interengaged needle and bobbin threads when said threads are withdrawn from about the trailing end of said bobbin case and while said dispensing location is substantially at its maximum spacing from said stitch-forming location and coordinated drive means for reciprocating said needle, rotating said bobbin case and actuating said tensioning means in timed relation to each other, wherein said drive means is arranged to rotate said bobbin case through two revolutions during each stitch-forming cycle, means operable during each stitch-forming cycle for alternately directing said bobbin thread to the opposite sides of said leading end of said bobbin case such that compensating twists are imparted to said bobbin thread during the two revolutions of said bobbin case in each stitch-forming cycle.

5. A method of forming a lock stitch with a needle thread and a bobbin thread comprising the steps of forming said bobbin thread into a crescent-shaped bobbin, forming said needle thread into a bobbin-receiving loop at a stitch-forming location, rotating said bobbin to pass said bobbin through said loop while said bobbin is oriented to present its minimum cross section to said loop to interengage said needle and bobbin threads and drawing up said needle thread to complete said lock stitch, said bobbin being turned through one revolution during formation of said needle thread into said bobbin-receiving loop and through a second revolution to pass said bobbin completely through said bobbin-receiving loop, said bobbin thread being directed to one side of said bobbin during said one revolution and to the other side thereof during said second revolution.

6. In a sewing machine, a needle movable through a stitch-forming cycle and adapted to receive a needle thread, a crescent-shaped bobbin case having leading and trailing ends spaced from each other and an internal chamber adapted to receive a supply of bobbin thread therein, means mounting said bobbin case for rotation about a bobbin axis, said mounting means being constructed and arranged to enable said needle thread to be cast about said leading end of said bobbin case, engaged with said bobbin thread and withdrawn from about said trailing end of said bobbin case, drive means for moving said needle and rotating said bobbin case in timed relation to each other, said drive means being arranged to rotate said bobbin case through two revolutions during each stitch-forming cycle, and means operable during each stitch-forming cycle for alternately directing said bobbin thread to the opposite sides of said leading end of said bobbin case such that compensating twists are imparted to said bobbin thread during the two revolutions of said bobbin case in each stitch-forming cycle.

7. A sewing machine comprising a needle movable through a stitch-forming cycle and adapted to receive a needle thread and present the same at a stitch-forming location, a crescent-shaped bobbin case having leading and trailing ends spaced from each other, an internal chamber adapted to receive a supply internal bobbin thread therein and an exit port from said internal chamber providing a dispensing location disposed diametrically in relation to the space between said leading and trailing ends, means mounting said bobbin case for rotation about a bobbin axis, said mounting means including circumferentially spaced mounting members constructed and arranged to enable said needle thread to be cast about said leading end of said bobbin case, engaged with said bobbin thread and withdrawn from about said trailing end of said bobbin case, said bobbin thread being withdrawn from said bobbin case incident to rotation thereof and presenting its maximum free length of said bobbin thread when said dispensing location is at its corresponding maximum spacing from said stitch-forming location, said leading end of said bobbin case serving as a hook and engaging said needle thread at said stitch-forming location, tensioning means engaging said needle thread and periodically operable for drawing up on the interengaged needle and bobbin threads when said threads are withdrawn from about the trailing end of said bobbin case and while said dispensing location is substantially at its maximum spacing from said stitch-forming location and coordinated drive means for reciprocating said needle, rotating said bobbin case and actuating said tensioning means in timed relation to each other, wherein said driving means is arranged to rotate said bobbin case through two revolutions during each stitch-forming cycle and including means operable during each stitch-forming cycle for alternately directing said bobbin thread to the opposite sides of said leading end of said bobbin case such that compensating twists are imparted to said bobbin thread during the two revolutions of said bobbin case in each stitch-forming cycle.

8. A sewing machine comprising a needle movable through a stitch-forming cycle and adapted to receive a needle thread and present the same at a stitch-forming location, a crescent-shaped bobbin case having leading and trailing ends spaced from each other, an internal chamber adapted to receive a supply of bobbin thread therein and an exit port from said internal chamber providing a dispensing location disposed diametrically in relation to the space between said leading and trailing ends, means mounting said bobbin case for rotation about a bobbin axis, said mounting means including circumferentially spaced mounting members constructed and arranged to enable said needle thread to be cast about said leading end of said bobbin case, engaged with said bobbin thread and withdrawn from about said trailing end of said bobbin case, said bobbin thread being withdrawn from said bobbin case incident to rotation thereof and presenting its maximum free length of said bobbin thread when said dispensing location is at its corresponding maximum spacing from said stitch-forming location, said leading end of said bobbin case serving as a hook and engaging said needle thread at said stitch-forming location, tensioning means engaging said needle thread and periodically operable for drawing up on the interengaged needle and bobbin threads when said threads are withdrawn from about the trailing end of said bobbin case and while said dispensing location is substantially at its maximum spacing from said stitch-forming location and coordinated drive means for reciprocating said needle, rotating said bobbin case and actuating said tensioning means in timed relation to each other, wherein said mounting means includes means for periodically moving said mounting members to a clearance position relative to said bobbin case to enable said needle thread to be cast about said bobbin case.